Guanting Reservoir (GR) is one of the most important water sources for Beijing and neighboring regions. Due to water pollution, it was withdrawn from the system to supply Beijing drinking water; however, after a thorough treatment process, GR was made a reserve water source since 2007. To develop a comprehensive and quantitative analysis of water yield and purification services in the GR watershed, this study selected two time periods: the period when GR was withdrawn from the system supplying local drinking water and the period that it has been designated a reserve water source. The InVEST model was used to evaluate the quantities of water yields, and total nitrogen and total phosphorus outputs from 1995 to 2010 Additionally, the spatiotemporal variations of water yield services and water quality purification services in the GR watershed were analyzed. The results showed that water yield services in the GR watershed first weakened and then became stronger, but weakened overall during the years 1995 to 2010. Water yield capacity in the basin decreased from 1.89×109 m3 in 1995 to 1.43×109 m3 in 2010 (a drop of 24.0％ in total). Water quality purification services also showed the same tendency. Total nitrogen output decreased from 4028.7 t in 1995 to 3611.4 t in 2010, while total phosphorus decreased from 379.7 t in 1995 to 354.0 t in 2010. Nitrogen and phosphorus purification services were enhanced by 10.4％ and 6.8％, respectively. Changes in the climate and land use were the main factors which lead to the changes in the water yield service in the GR watershed. Policies intended to protect water resource have matched the varying trends of water quality purification services during different periods. On one hand, the research results provide a foundation to identify key fields for eco-compensation in the Guanting Reservoir basin. On another hand, the ecosystem service value will increase on the basis of eco-compensation criteria through setting the scenarios of returning farmland to forest and ecological protection. This method directly reflects increases in ecosystem service values that have occurred since measures to protect the ecological environment have been implemented. This method is more persuasive and feasible than using eco-compensation criteria based on regional ecosystem service values determined by land use/ coverage type. It can provide a new way to assess eco-compensation in the Guanting Reservoir basin and other regions.%官厅水库(GR)是北京及其周边地区最重要的水源地之一,曾因水质污染严重而被迫退出北京市饮用水供应系统,经过全面治理后于2007年恢复成为北京市备用水源地.为了从整体上定量分析官厅水库流域生态系统的产水和水质净化服务,基于InVEST模型,选择官厅水库退出北京市饮用水供应系统和恢复成为北京市备用水源地为时间节点,定量评估1995—2010年官厅水库流域生态系统的产水量和TN、TP输出量,分析其产水服务和水质净化服务的时空变化.结果表明:1995年至2010年,官厅水库的产水服务服务先减弱后增强,整体呈现减弱趋势,流域产水量从1995年的1.89×109 m3降至2010年的1.43×109 m3,产水服务减弱24.0％,水质净化服务表现为先减弱后增强,但整体呈增强趋势.TN产量从1995年的4028.7吨下降到2010年的3611.4吨,TP从1995年的379.7吨下降到2010年的354.0吨.TN和TP净化服务分别增加了10.4％和6.8％.研究显示,气候和土地利用的变化是导致官厅水库水利服务变化的主要因素,不同时期的水资源保护政策导向也与水质净化服务变化趋势相吻合.一方面,以上研究成果可以为确定官厅水库流域生态补偿的关键领域奠定基础,另一方面,通过设定退耕还林还草和生态保护的目标情景,在这个目标情景作为生态补偿标准的基础上,可以获得生态系统服务价值的增量.这种方法直接反映了自生态环境得到保护以来新增的生态系统服务价值,这与土地利用/覆盖类型视角下,基于区域生态系统服务价值的生态补偿标准相比,更具说服力和可行性,并且为官厅水库流域及其他地区的生态补偿提供了新的途径.
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